This invention relates to the field of image reading technology for typical use with digital photoprinters that read film images photoelectrically to produce prints (photographs) reproducing the images.
Heretofore, the images recorded on photographic films such as negatives and reversals (which are hereinafter referred to simply as "films") have been commonly printed on light-sensitive materials (photographic paper) by means of direct (analog) exposure in which the film image is projected onto the light-sensitive material to achieve its areal exposure.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, the image recorded on a film is read photoelectrically, converted to digital image data (image signals) and subjected to various image processing schemes to produce image data (output image signals) for recording purposes; recording light that has been modulated in accordance with the image data (output image signals) is used to scan and expose a light-sensitive material to record a latent image, which is subsequently developed to produce a (finished) print. The printer operating on this principle has been commercialized as a digital photoprinter.
In the digital photoprinter, images are converted to digital image data that are processed to determine the exposing conditions for printing. Hence, the digital photoprinter is capable of performing effective image processing operations such as the correction of washed-out highlights or flat shadows due to the taking of pictures with back light or an electronic flash, sharpening and the correction of color or density failure and this enables the production of high-quality prints that have been impossible to attain by the conventional direct exposure technique. In addition, not only the assembling of plural images and the dividing of a single image but also the compositing of characters on image can be performed by processing the image data and, as a result, prints can be output after various editing and/or processing operations have been performed in accordance with specific uses.
Outputting images as prints (photographs) is not the sole capability of the digital photoprinter; the image data can be supplied into a computer or the like and stored in recording media such as a floppy disk; hence, the image data can be put to various non-photographic uses.
Having these features, the digital photoprinter is basically composed of an image input machine having a scanner (image reading apparatus) and an image processing apparatus, and an image output machine having a printer (an image recording apparatus) and a processor (developing apparatus).
In the scanner, reading light issuing from a light source is allowed to be incident on a film, from which projected light bearing the image recorded on the film is produced and focused by an imaging lens to form a sharp image on an image sensor such as a CCD sensor; the image is then captured by photoelectric conversion and sent to the image processing apparatus as image data for the film (i.e., image data signals) after being optionally subjected to various image processing steps.
In the image processing apparatus, image processing conditions are set on the basis of the image data read with the scanner and image processing as determined by the thus set conditions is performed on the thus read image data and the resulting output image data (output image signals) for image recording are sent to the printer as the exposing conditions.
In the printer, if it is of a type that relies upon exposure by scanning with a light beam, the latter is modulated in accordance with the image data sent from the image processing apparatus and deflected in a main scanning direction as a light-sensitive material is transported in an auxiliary scanning direction perpendicular to the main scanning direction, whereby a latent image is formed as the result of exposure (printing) of the light-sensitive material with the image bearing light beam. Development and other processing as determined in accordance with the light-sensitive material are then performed in the processor to produce a print (photograph) reproducing the image that was recorded on the film.
Not only in the scanner used in the digital photoprinter described above, but also in an image reading apparatus in a system which requires outputting high quality images, it is preferred to capture the densities of the original image at the highest possible density resolution. To this end, image reading need be performed making the best use of the dynamic range of an image sensor such as a CCD sensor provided in the scanner.
Therefore, many apparatuses perform prescan for roughly reading the image prior to fine scan for obtaining output image data for printing purposes. The image data obtained by prescan is used to find the density range or the like of the image, in accordance with which the reading conditions for fine scan as well as the processing conditions of the image data obtained by fine scan (or image processing conditions) are determined.
Therefore, prescan is performed under the condition that all the densities that may be used for recording on an original can be captured. Namely, if a negative film is used as the original, it is required in prescan mode to properly and precisely read the image having a density range so wide as to exceed 3 in terms of the density, including from an under-exposed original to an over-exposed original.
However, there are few image sensors with a wide dynamic range that can read the image having such a wide density range with high precision.
In an apparatus which requires image reading in a density range exceeding the dynamic range of the image sensor capable of proper reading with high precision, a plurality of reading operations advantageously adapted for the images having different density ranges are performed in prescan mode under the reading conditions different in the light quantity as obtained by changing the storage time (exposure time) of the CCD sensor. Based on the results of prescan, it is possible for example to adopt prescanned data obtained under the reading conditions which achieved proper reading, thereby determining the reading conditions for fine scan and the image processing conditions.
In order to reproduce a film image as an output image of higher quality, it is preferred to determine the reading conditions for fine scan and the image processing conditions taking into consideration the film properties including, for example, the base density of the film.
It is difficult to obtain the proper film properties from the image data of one frame. Then, it is preferred to use the image data of a plurality of frames, more preferably of all the frames of a film to thereby find the film properties. That is, the image data of a plurality of frames need be used to set more advantageous reading conditions for fine scan and image processing conditions in view of the film properties.
However, if prescanned data of a plurality of frames obtained under different reading conditions exist, they can not be treated as the identical data when used to set the image processing conditions or the reading conditions for fine scan. Then, setting of the proper reading conditions for fine scan and image processing conditions is not possible.
Even if differences between the prescanned data of the plurality of frames due to the reading conditions for prescan are simply cancelled, there are many cases in which proper image processing conditions or reading conditions for fine scan cannot be set because of the properties of the image sensor including the CCD sensor.